Vehicle roof systems also known as sunroof systems are widely used in passenger vehicles for selectively opening and closing an opening formed in the roof of the vehicle. A typical vehicle roof system comprises a moveable roof panel and a drive unit for actuating the moveable roof panel between a position to close the opening and a position to expose the opening. A pair of guide rails are fixedly secured to the fixed roof panel, and extend along either lateral side of the roof opening, and the moveable roof panel is supported by these guide rails via sliders so as to be slidable in the fore and aft direction. An electric motor is provided centrally on the front edge of the roof opening, and a pair of push-pull cables connected to the corresponding sliders are actuated by the electric motor as required.
The push-pull cable used for such a vehicle roof system typically consists of a flexible steel core wire having another cable wound spirally around the core wire or a plastic belt having a rack gear formed on one side thereof. In a vehicle roof system, each push-pull cable is linearly guided along a cable guide formed in the corresponding side frame, and guided by a curved guide pipe (a drive pipe) secured to a front frame from the front end of the cable guide to the drive gear of the electric motor. The idle cable section of each push-pull cable extending from the drive gear to the free end of the push-pull cable is also guided by a guide pipe (an idle pipe). As the two push-pull cables are required to be synchronized for the smooth actuation of the moveable roof panel, it is essential that the two push-pull cables are guided along the prescribed paths at all times.
The guide pipes were conventionally made of steel pipe, and it was proposed to make the idle pipe from plastic material so that the bending work of the pipe may be simplified. The drive pipes are made of steel, and extend along a common plane, while the idle pipes are made of soft plastic material so that the generation of noises may be avoided when the drive pipe and idle pipe strike each other due to the vibrations of the vehicle body. See Japanese patent No. 3043589 (patent document 1).
It was also proposed to form guides pipes integrally with the front frame made of plastic material for guiding the push-pull cables therein. See Japanese patent No. 3994815 (patent document 2).
However, according to the proposal in patent document 1, as the drive pipes are made of steel, there still is the need to conduct a relatively costly bending work, and no significant weight reduction can be accomplished. Also, because the drive pipe extends beyond the front edge of the front frame, some care is required in handling the drive pipe or the assembly incorporated with the drive pipe so as not to bend it.
The proposal in patent document 2 eliminates the need for the guide pipes, and reduces the number of component parts. However, the die assembly for molding the front frame becomes more complex, and this increases the manufacturing cost. Also, because the guide pipe portions formed in the front frame do not entirely cover the push-pull cables, lubricating grease cannot be contained within the guide pipe portions, and an adequately smooth guide surfaces may not be defined.
Furthermore, when the guide pipe portions are formed integrally with the front frame, the radius of curvature cannot be reduced so much as in the case of more conventional steel guide pipes. The resulting increase in the frictional resistance requires the use a more powerful electric motor, and this in turn causes the thickness of the vehicle roof to be increased. Also, a large radius of curvature requires the fore-and-aft dimension of the front frame to be increased, and this necessitates the front edge of the roof opening to be placed more rearward than desired. If the roof opening is located too far back in the roof, the viewing angle of the vehicle occupant through the roof opening is so upright that the vehicle occupant's field of view is restricted, and the benefits of the sunroof system are diminished.